Our major objective is to elucidate the mechanism(s) by which estrogens control the release of luteinizing hormone-releasing hormone (LHRH) in the hypothalamus. To accomplish this objective we have developed an in vitro model for studying LHRH secretion which consists of synaptosomes isolated from the basal medial hypothalamus of rats. Synaptosomes are employed to test the following hypothesis: estrogens (E) exert their influence on the hypothalamus via specific receptors which (1) translocate to nuclei neurons as receptor-estrogen complexes, and (2) initiate the synthesis of "hypothalamic mediator protein(s)" which in turn inhibit(s) the release of LHRH. BIBLIOGRAPHIC REFERENCES: "In Pursuit of the GABA Receptor," Peck, E.J., Jr., Schaeffer, J. M., and Clark, J. H. in GABA in Nervous System Function, Roberts, E., Chase, T.N., and Tower, D.B. (eds.). Raven Press, New York, 1975, pp. 319-336. "Hypothalamic Synaptosomers and In Vitro (LRF Secretion," Peck, E.J., Jr., Tytell, M., and Clark, J. H. Prog. 57th Meeting, The Endocrine Society, #89, 1975.